MXPA96004787A - Catalysts for the production of phenol and its deriva - Google Patents

Abstract

Zeoliteutile catalysts are disclosed for the production of phenol and its derivatives by the oxidative hydroxylation of benzene and its derivatives by nitrous oxide, e.g., at temperatures of 225-450 ° C, having substantially improved process characteristics resulting from the hydrothermal treatment, using a gas containing from about 3 to 100 mole% water vapor, v.gr, at a temperature ranging from about 500 to 1000øC. Two hours of hydrothermal treatment have been shown to be effective

Description

CATALYSTS FOR THE PRODUCTION OF FENOL AND ITS DERIVATIVES DESCRIPTION OF THE INVENTION Improved catalysts for the production of phenol and its derivatives by the one-step oxidative hydroxylation of benzene or other aromatics by nitrous oxide, and methods for making such catalysts are disclosed herein.

BACKGROUND The production of phenol by the partial oxidation of benzene using nitrous oxide has been described on a wide variety of catalysts ranging from vanadium pentoxide on silica to zeolites, e.g., zeolite catalysts of ZSFI-5 and ZSM- 11, at elevated temperatures, e.g., of 300 to 450 ° C. When the benzene is replaced by a benzene derivative, such as chlorobenzene, f luorobenzene, toluene or ethylbenzene, the corresponding substituted phenol can be produced. When the benzene by itself is substituted benzene, the reaction products include dihydroxybenzene, such as hydroquinone, resorcinol and catechol. Phenol and its derivatives, for example, dihydric phenols, chlorophenols, piphophenols, cresols and other aromatic compounds containing hydroxyl, are valuable products that find wide applications in the industry. The most common chemical of this kind is phenol, which is used mainly in the production of phenolic resins, caprolactam, nitrophenols and chlorophenols, etc. For decades, researchers have searched for simple and efficient methods for the synthesis of phenol and its derivatives. Iwamoto et al., In 3. Physical Chemistrv (ACS), Vol. Ñ7, No. 6, (1963), p. 903.905, reported that the single-step hydroxylation of aromatic compounds can be effected using nitrous oxide as an oxidant, in the presence of traditional catalysts for partial oxidation, eg, supported oxides of vanadium, molybdenum and tungsten. The amotole drove the reaction at 550 ° C with the benzene conversion of 10% 'and selectivity to the 72% phenol. Although these results were far superior to all the previous achievements, they are still insufficient for the practical use of the procedure, which dictated the need to look for more efficient systems. The use of the new type of catalyst, eg, aluminosilicates with a high silica content, with a zeolite structure, for the hydrolation of benzene, was reported by Suzuki et al., In Chemical Society * of Japan's Chemistry Letters. (19fiA), p. 953-956; by Gubel ann and others, in the North American patent. 5,055,623; and by Kharitonov and others, in the North American patent. 5,110,995. In the presence of such zeolite catalysts, the hydroxylation of benzene and other aromatic compounds occurs at 300-400 ° C, with a phenol selectivity of 90-100%. However, the activity of the catalyst remains sufficiently inadequate for the commercial practice of this technology. Researchers continue to discover new ways to improve the parameters of the procedure and / or improve the efficiency of the zeolitae, e.g., by introducing various types of catalyst pretreatment. In this regard, Zholobenko reported in Mendeleey Commun .. (1993) No. 1, p. 2d-29, a method to produce phenol, using a zeolite catalyst, which has been activated by calcination, at high temperature, in the air. A disadvantage of this Zholobenko method is that it does not provide any increase in catalyst activity at the calcination temperature, below 700 ° C. More particularly, since the effect of activation is significant at higher temperatures (750 ° C, and above), the Zholobenko method is difficult to implement practically.

BRIEF DESCRIPTION OF THE INVENTION This invention solves the various problems associated with insufficient efficiency and efficiency of zeolite catalysts in the hydroxylation, with nitrous oxide, of benzene and its derivatives in the production of phenol and its derivatives. These problems are surprisingly solved by the use of a zeolite catalyst which is activated by a simple and efficient method, e.g., exposure to water vapor at elevated temperature.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES This invention provides an improved zeolite catalyst for the production of phenol and its derivatives, by hydroxylation of the corresponding aromatic compounds using nitrous oxide. The properties of the catalytic performance of said zeolite catalysts are improved using the methods of this invention, treating the zeolite catalyst with a gas phase containing steam, at a temperature in the range of 350 to 950 ° C. The amount of water vapor in the gas phase is not critical and can vary from a low level of water vapor in a diluent gas to essentially pure water vapor. For example, the gas phase may vary ranging from as little as 3 mol% (grit) of water vapor in the air, or preferably in a gas phase of substantially inert diluent comprising nitrogen, argon, helium, carbon dioxide, and similar, or mixtures thereof. Of course, the gas phase must be essentially free of components that tend to poison the catalysts. The gas phase may preferably comprise larger amounts of water vapor, e.g., 10 mol% or more, up to 100 mol%. The duration of high temperature exposure of the steam water catalyst may vary, depending on the desired improvement and can be easily determined by routine experimentation. The zeolites subject to improvement by the method of this invention include zealites of ZSM-5 and ZSM-11, which preferably are in the acid form and contain iron. Said zeolites are well known in the art, are used for a variety of commercial processes, and can be easily obtained from catalysts sellers, such as UOP, Mobil and others. Commercial zeolite catalysts are typically provided in a porous matrix of alumina or silica, to provide a durable pellet form, which resists wear in packed or fluid bed reactors. It has been found that the method of this invention can be successfully applied to powdered or pelletized zeolite. The improved yield zeolite catalysts prepared by the method of this invention are especially useful in the oxidation of aromatic compounds, such as benzene and benzene derivatives, e.g., chlorobenzene, fluorobenzene, toluene, ethylbenzene and the like, including phenol. Said oxidation is effected by passing a mixture of phenol feed gas, nitrous oxide and, optionally, diluent gas, such as nitrogen, argon, carbon dioxide, and the like, to a bed of zeolite catalyst at a temperature on the scale from 225 to 450 ° C, or higher, eg, above 500 ° C. The process conditions, including the feed composition, the reaction temperature, the flow rates and the like, can be varied by those skilled in the art, depending on the desired process parameters, e.g., selectivity of the production of phenol, conversion of nitrous oxide, concentration of phenol in the product gas, catalyst productivity, and the like. For example, the molar ratio of nitrous oxide to benzene in the feed mixture can vary from 100: 1 to 1: 100. In certain preferred embodiments, there are advantages to operating the process with a molar excess of the aromatic compound. In one aspect of this invention, zeolite catalysts which have been hydrothermally treated are characterized by a stable yield in a desired catalytic conversion, ie, low reduction of benzene conversion in phenol production by oxidation of benzene with nitrous oxide at 350 ° C. The preferred catalysts of this invention, eg, ZSM-5 or ZSM-11 zeolite catalysts, will exhibit a benzene conversion ratio after 3 hours of continuous operation for the initial conversion of benzene to at least 40%. . In more preferred catalysts the ratio will be at least 50%. The following examples illustrate catalysts, wherein said ratio is about 70%.

The catalysts of this invention that have been hydrothermally treated can be identified by resistance to idthermal treatment. For example, a zeolite, iron-containing zeolite catalyst, of this invention, can be characterized in that the hydrothermal treatment of said catalyst, for two hours with a gas consisting of 50 mole% air and 50 mole% water and a temperature of 600 ° C, the benzene conversion efficiency of the catalyst is not increased by more than 10%, when it is used in the catalytic hydroxylation of benzene to phenol in a gas stream consisting of 75 mol% of helium, 5% molar of benzene and 20 mol% of nitrous oxide, at 35 ° C. The advantages of this invention are illustrated by the following examples, wherein the improved yield of the zeolites is demonstrated by the oxidation of benzene using nitrous oxide.

EXAMPLE 1 A zeolite catalyst based on Si02, containing 4.3 x 10 ***** moles of Fea0a and 2.3 x 10 *** - 2 moles of Ala0a, was prepared according to the methods described by Kharitonov in US Patent 5,110,995. , per mole of Si02. After the organic template material was burned, the zeolite was treated with acid to transform it into the H form and was calcined in a flow of dry air at 550 ° C for two hours. For the catalytic property test, a tubular reactor was prepared, charging approximately 2cc of a 0.5-1.0 mm fraction of the zeolite to a quartz tube, with an internal diameter of 0.7 cm. The tubular reactor filled with zeolite was heated to 350 ° C and fed with a reaction gas mixture comprising 5 mol% benzene and 20 mol% nitrous oxide in helium. The product gas flowing from the reactor was periodically analyzed by gas chromatography. The gas analysis data were used to calculate benzene conversion (X) and selectivity to phenol < S > , which are reported in Table 1. It was observed that the catalyst was apparently deactivated during the operation due to the deposition of coke. Measurements were taken, 20 minutes after the start of the feed gas flow to the reactor, to determine an initial conversion of benzene, Xot of ß.5% and an initial selectivity, So? of 92.5%. After 3 hours of continuous operation, the benzene conversion was determined and this was 3.0%, indicating a reduction in the catalytic activity. The ratio of benzene conversion to the initial conversion of benzene (X / X0) of 35% characterized the stability of the catalyst during operation. No reduction in selectivity was observed during any of the operations.

EXAMPLE 2 The catalyst, prepared substantially in the manner described in Example 1, was further subjected to hydrothermal treatment for two hours, exposing it to air containing 50 mole% of water at 500 ° C for two hours, in the presence of air containing 50 mole% of Water. The catalytic properties of the hydrothermally treated catalyst, reported in Table 1, show a substantial increase in the initial conversion of benzene to 1A.5%. EXAMPLE 3-ß These examples illustrate aspects of the invention, wherein the temperature of the hydrothermal treatment is varied. In these examples, catalyst samples were prepared, in essentially the same manner as in Example 2, except that the hydrothermal treatment was carried out at 550-1000 ° C. The observed catalytic properties, reported in Table 1, show that an optimum hydrothermal treatment temperature can easily be determined by routine experimentation to provide a catalyst with the desired initial or long-term conversion characteristics. More surprisingly, as the conversion of benzene increases with the hydrothermal treatment, eg, from fi.5% to 37%, the stability of the catalyst is also increased by a factor of 2, e.g., X / X0 increases from 35% to 70%. Said treatment, at a very high temperature, e.g., around 1000 ° C, is not advisable, since it apparently leads to a reduction in activity.

TABLE 1 EXAMPLES 9-12 These examples illustrate aspects of this invention, wherein the water content of the hydrothermal treatment is varied. In these examples, catalyst samples were prepared in essentially the same manner as Example 2, except that the hydrothermal treatment was carried out with a treatment gas at 600 ° C and containing 2.5 to 100 mole% of water vapor. The catalytic data reported in Table 2 show that by increasing the concentration of water vapor in the hydrothermal treatment, the gas can provide a catalyst with a substantially improved process efficiency. For example, benzene conversion increased from 6.6% to 38.5%, with a simultaneous increase in stability and some increase in selectivity. In Example 9, the hydrothermal treatment was carried out under conditions potentially similar to the calcination of the catalyst in air, e.g., at 2.5 mole% of water vapor. The comparison of Examples 9 and 1 shows that said water concentration is not sufficient for a marked activation of the catalyst. f - TABLE 2 EXAMPLE 14-16 These examples illustrate the beneficial effect of the process of this invention on a variety of catalysts useful in the hydroxylation of benzene using nitrous oxide to produce phenol. Zeolites were evaluated with a composition reported in Table 3, to determine an initial conversion of benzene and a selectivity of phenol. Then, the zeolites were hydrothermally treated, exposing them, for two hours, to a gas at 500 ° C containing 50 mol% of water. It can be seen that said hydrothermal treatment substantially improves the process characteristics of said varied zeolite compositions.

TABLE 3 These examples show the essence of the proposed invention, but in no way exclusive, meaning that the optimum conditions of hydrothermal activation (temperature, time, water vapor concentration, etc.) may be different for different types of catalysts and intended reactions for the use of the catalyst. In particular, the high efficiency of the activated catalysts makes it possible to carry out the process, not only with an excess of nitrous oxide, but also with an excess of aromatic species, e.g., until the molar ratio of the aromatic species to nitrous oxide is 100: 1. The advantage of carrying out the process with an excess of the aromatic compound is that, under such conditions, a complete conversion of the nitrous oxide is achieved. This leads to a significant simplification of the technology, since, in this case, it is not necessary to isolate the unreacted nitrous oxide and return it to the reaction. Since specific embodiments have been described herein, it should be apparent to those skilled in the art that various modi fi cations to the same can be made, without departing from the true spirit and scope of the invention. Accordingly, it is intended that the following claims cover all these features within the full concept of the invention.

Claims (7)

NOVELTY OF THE INVENTION CLAIMS

1. A method for preparing a zeolite catalyst for the improved oxidation of benzene with nitrous oxide, characterized in that it comprises hydrothermally treating a zeolite catalyst with a gas comprising from 3 to 100 mol% of water, at a temperature of 350 to 950 ° C .

2. A method according to claim 1, further characterized in that said zealite catalyst is a zeolite catalyst of ZSM-5 or ZSM-li.

3. A method according to claim 2, further characterized in that said catalyst is an acidified, iron-containing zeolite.

4. A method according to claim 3, further characterized in that said gas comprises at least 10 mol% of water.

5. A method according to claim 4, characterized in that said gae is at a temperature of at least 500 ° C.

6. A zeolite catalyst of ZSM-5 or ZSM-11 characterized by the stable conversion of benzene in the production of phenol, by the oxidation of benzene with nitrous oxide at 350 ° C, wherein the ratio of benzene conversion, after 3 hours of continuous operation, at the initial benzene coprection ee at least 40%.

7. An acidified zeolite catalyst, containing iron, characterized in that the hydrothermal treatment of said catalyst, for two hours with a gas consisting of 50 mol% of air and 50 mol% of water, and at a temperature of 600 ° C, does not increases by more than 10% the conversion efficiency of benzene from the catalyst, when used in the catalytic hydroxylation of benzene to phenol in a gas stream connecting 75% molar of helium, 5% molar of benzene and 20% molar of nitrous oxide, at 350 ° C.